1. Field of the Invention
The present invention relates to an electrophotographic image forming apparatus, and more particularly, to an image forming apparatus including a lubricant applying section that applies a lubricant to image bearing members such as a photoconductor and an intermediate transfer member.
2. Description of Related Art
In general, electrophotographic image forming apparatus (such as printers, copiers, and facsimile machines) are configured to irradiate (expose) a charged photoconductor with laser light according to the image data to form thereon an electrostatic latent image. The electrostatic latent image is then visualized by supplying toner from a developing device to the photoconductor (image bearing member) on which the electrostatic latent image is formed, whereby a toner image is formed. The toner image is then directly or indirectly transferred onto a sheet, heated and pressurized for fixing to form an image on the sheet.
Toner that remains on the surface of a photoconductor drum after transfer (i.e., residual toner) is collected by a cleaning device. The cleaning device includes a cleaning blade that is made of an elastic body and is placed in sliding contact with the surface of the photoconductor drum. The residual toner is scraped by the cleaning blade, whereby the surface of the photoconductor drum is cleaned.
In the cleaning process, because the photoconductor drum is rotated with the cleaning blade being in sliding contact therewith, a frictional force is generated at the sliding-contact portion between the photoconductor drum and the cleaning blade, resulting in unwanted ablation of the photoconductor drum and cleaning blade. In an effort to reduce such a frictional force at the sliding-contact portion, image forming apparatus have been proposed that are configured to apply a lubricant to the surface of the photoconductor drum (see, e.g., Japanese Patent Application Laid-Open Nos. 2011-180397 and 2007-193183).
In general, when a lubricant is applied to a photoconductor drum, a lubricant applying brush is fixed in sliding contact with the photoconductor drum, and a solid lubricant is placed so as to be pressed against the lubricant applying brush. The lubricant applying brush is then rotated allowing the solid lubricant to be scraped off and applied to the photoconductor drum.
The solid lubricant is formed as a column for example by the gravity casting method, wherein a cylindrical mold is placed upright such that the axial direction thereof is vertical, a liquid resin is poured into the mold so as to fill the mold by its weight, and the resin is allowed to solidify.
Upon production of a solid lubricant by the gravity casting method, dissolved gas appears in the form of gas bubbles during the solidification of the resin. As the resin gradually solidifies from the bottom side, the gas bubbles migrate upward through the resin to the surface. However, some of the gas bubbles remain trapped in the resin. Accordingly, while one end in the axial direction of the solid lubricant (hereinafter, bottom-side end) corresponding to the bottom side during the production of the solid lubricant is formed in solid form, at the other end in the axial direction of the solid lubricant (hereinafter, pouring-side end) corresponding to the top side (pouring side) during the manufacture of the solid lubricant, gas bubbles remain trapped, and so-called blowholes are likely to occur. That is, the lubricant density of the pouring-side end is lower than that of the bottom-side end due to the occurrence of the blowholes.
In recent years, a photoconductor drum unit unitized by including a photoconductor drum, a cleaning device, and the like is required to have a longer service life. In order to meet this requirement, an increase in size of a solid lubricant has been developed. Consequently, blowholes are further likely to occur in the pouring-side end of the solid lubricant.
If blowholes occur in the solid lubricant as described above, the amount of lubricant applied to the photoconductor drum becomes partially insufficient, and abrasion and deterioration of the photoconductor drum or the cleaning blade are accelerated. Further, in order to achieve still higher definition and higher image quality, more uniform lubricant application is required, but it is unfortunately difficult to meet this requirement.